Distillation



May 30, 1939 B. G. ALDRIDGE ET Al. 2,160,256

ISISTILLATION original Filed July 1o, 1954 mm Nm um TSN S SQ Ew a EEPROM.m wat@ IN V EN TORS Bla z'r G. larldge 45 Edward/Pgaz Patented May 30,1939 UNITED STATES PATENT OFFICE DISTILLATION` Original application July10, 1934, Serial No. 734,529. Divided and this application August 26,1935, Serial No. 37,980.

ber 27, 1937 Claims.

This invention relates to fractional distillation of oil, andparticularly to vacuum distillation of hydrocarbon oils to producelubricating oil distillates, and is a division of our copending appli- 5cation Serial No. 734,529, filed July l0, 1934.

It is an object of this invention to provide a method 'of control whichwill automatically take care of variations in heat and feed input to afractional distillation system.

It is another object of this invention to eliminate the troublesometubular oil condenser ordinarily employed for condensation of theoverhead fractionated vapors and to substitute therefor a means ofcondensingthe overhead vapors by directly contacting them with cooledrecycled oil in a heat exchange tray section in communication with thefractionating system.

It is another object of this invention to provide a method forinitially-establishing operating conditions within a system whichutilizes a heat exchange section associated with the fractionatingcolumn in which condensation of the vapors is accomplished by directcontact with cooled oil.

It is another object of this invention to increase the distillationcapacity of the distillation system and to avoid undesirabledecomposition of the heated feed oil by recirculation therewith throughthe heater of a quantity of unvaporized oil from the flash section ofthe fractionating column.

It is another object of this invention to reduce or substantiallyeliminate the corrosion in the heating system normally attendant uponthe caustic solution treatment of the heated feed materials.

This invention resides in a process and apparatus for the fractionaldistillation of hydrocarbon oils to produce lubricating oil distillateswherein the fractionated vapors are totally condensed by directlycontacting them with a cooled circulating oil, and wherein control ofthe fractionating system is'maintained to allow for variations inquantity of heat and feed input by automatically returning to thefractionating column 4.5 a quantity of reflux sufficient to compensatefor this variation, and wherein the distillation capacity of thedistillation system is substantially increased by recirculation throughthe heater with the feed a quantity of unvaporized oil from the flashsection of the fractionating system, and wherein corrosion of thedistillation system, and particularly the heater, is reduced orsubstantially eliminated by the introduction of caustic solution intothe heated feed at a point between the heater and the flash section ofthe fractionating system,

Renewed Decemwhereby theA caustic solutionisrpermitted to flash out ofcontactwith the heater surfaces and wherebyV the thus flashedv causticis returned through the medium. of the recirculating oil from the flashsection of the fractionating column to the heater.

Figure 1, ispan enlarged diagrammatic view of the connections forintroducing caustic solution into the system.

Figure 2y comprises a diagrammatic illustration of the preferredapparatus by which the process of this invention is carried on, in whichI-l is a heater for providing a heated oil feed to the Afractionatingcolumn, S, includingk plates I, 2 and 3, is the stripping section, F,including plates 4 to I3 is the fractionating section, E, includingplates I4 and I5, is the heat exchange section, and the space betweenplates 3v and tinto which the feed is introduced is the separating orflash section. B illustrates a barometric condenser and steam ejectorsystem for maintaining a vacuum in the fractionating. and strippingsystem. T is a surge tank with a oatcontrol therein for accumulating andautomatically regulating the return of reflux to the fractionatingsystem. SI, S2 and S3; are stripping columns in which intermediatedistillate cuts received from the fractionating system are stripped oftheir light components to produce stripped lubricatingv oilvvdistillates. C is aV caustic storage tank from which caustic solution iswithdrawn and introduced into the heated hydrocarbonk feed to thefractionating column.`

The operation is as follows: v

Preheated lubricating oil stock feedis introducedA by means ofpumpv20through lines 2| and 22 into the convection section of the heating tubes23 of; the heater H. The partiallyl heated feed is. finally. heated inthe radianttubular section 25-in the heater Hand from there is intro:duced into the hash section of the. fractionating column through lines26 and 2'I and inlet 28. The thus heated oil falls uponl and flowsacross plate 3 where it is intimately contactedy with rising steam andhydrocarbon vapors from the stripping section S therebelow. Upon thusvcontacting the said steam and vaporsthe heated oil feed is partiallyflashed into .vapors which in turn pass upwardv through thefractionating section F of the fractionating column inY countercurrentcontact with reflux condensate resulting in the fractionation of thesaid vapors.

A portion of theunvaporized oil from the hash section of thefractionating` column iswithdrawn at wand-.reintroduced bymeans of pump3| and line 32 intotheheatingsection 25 where it meets andA mixes withthej partially heated feed from heating section 23. The mixture of thenew heated lubricating oil feed stock and the recirculated oil from theflash section of the column thus constitutes the feed introduced to thesaid lines 26 and 21 and inlet 28.

The unvaporized oil not withdrawn through 30 from the flash sectioncontinues downward over trays 2 and I of the stripping section S incountercurrent to steam to further strip light components therefrom, andthe residual oil result# ing therefrom is withdrawn through outlet 35,float control valve 36 and bottoms disposal line 31. A float control 38serves to regulate valve 36 to maintain a constant residuum liquid levelin the bottom of the stripping section S.

The fractionated vapors leavingthe top trays I3 of thefractionatingsection F of the fractionating column pass into the heatexchange section E comprising plates |4 and |5 where the said vapors aresubstantially totally condensed in contact with cooled recycled gas oil.The cooled recycled gas oil containing the commingled condensate formedin the heat exchange section E is Withdrawn from plate |4 through outletline 40, valve 4| and line 42 to the surge tank T from which it iswithdrawn through valve 45 and forced by means of pump 46 through thecooler 41. The flow of the thus cooled gas oil is split in three Ways, apredetermined quantity controlled by valve 50 being withdrawn toproduction through line 5|, a predetermined ccnstant quantity determinedby the setting of valve 52 being returned through line 53 to the heatexchange section E to contact and condense the vapors from thefractionating section of the column as hereinbefore disclosed, and thebalance of the gas oil being returned through lines 55 and 51 asregulated by the oat control valve 56 for reflux to the top of thefractionating section The air, fixed gases and entrained oil vapors arewithdrawn from the top of the fractionating column through line 60 tothe condensing system B in which a barometric condenser 6| is providedfor condensing the steam and entrained vapors and a steam ejector 63 isprovided for exhausting the said barometric condenser of the air and xedgases. Water, preferably. salt water, is supplied to the barometriccondenser and thesteam ejector through lines 65 and 66. Thewater-withdrawn from the barometric condenser leg, and thelexhaust ofthe steam ejector is Withdrawn from the tank 61 through outlet 68. Steamis supplied to the steam ejector through steam line 10.

Intermediate side cuts of descending reux condensate are withdrawn fromthe fractionating section F of the column through linesY 15, 16 and 11to stripping columns Si, S2 and S3 respectively. rIhe trays from whichthe said withdrawn side cuts are taken are regulated by the valves 1Sand 80 for stripper No. 1, 8| and 82 for a stripper No. 2, and 83 and 84for stripper No. 3. Other connections may be provided so that side cutsmay be taken from any of the trays in the column desired. The thusWithdrawn side cuts are stripped of their light constituents incountercurrent contact with steam which is introduced at the bottoms ofthe stripping columns as shown at 85 in column Sl. The combined strippedvapors and steam pass from the stripping columns through line 81 intothe condenser 89 and Athe resulting condensate collected in receiver 90.The condensate from receiver 90 is returned bymeans lof pump 92 throughline 93 and returned to the feed stream entering the heater through line22 and is reintroduced there- With into the fractionating system. Thefixed uncondensed gases from receiver 90 are exhausted by means of thebarometric condenser system B through line 95 which at the same timemaintains the side cut stripping system under vacuum.

The stripped side cuts are withdrawn from the bottoms of the strippingcolumns to storage and constitute the untreated lube oil distillates.For example, the stripped bottoms from stripping column SI is Withdrawnby means of pump 91 through outlet 98 through valve 99, cooler |00, andnally through line to storage. The rates of withdrawal of the bottomsfrom the stripping columns are regulated by the bottoms valves to apredetermined constant quantity. Float controls |02, |04 and |06 actupon valves |03, and |01 respectively to regulate the quantity of sidecut withdrawn from the fractionating column to the stripping columns S|,S2 and S3 respectively to maintain constant liquid levels in the bottomsof the said stripping columns.

In some cases where deep cuts of lubricating oil distillate are desired,the control of the withdrawal of condensate from the column to thestripper S3 may be transferred from valve |01 to valve |08. With thisarrangement valve |01 is maintained open and all of the descendingreflux condensate is withdrawn from the lower end of the fractionatingcolumn to the said stripping column S3, and valve |08 is controlled byfloat control |06 to remove the stripped oil as fast as it is receivedin the bottom of the stripper. In this case no reflux condensate isreturned to the flash section or stripping section of the column.

It has been found to be advantageous to circulate heavy oil through theheater with the feed material to the extent of one and one-half to threetimes the feed rate primarily, other conditions being established, tomaintain the desired temperature of the fiash tray. In recirculating thesaid unvaporized heavy oil through the heater it is advantageous towithdraw, for that purpose, the unvaporized oil from the flash tray inthe bottom of the flash section of the column, which in this case is theoil from the top tray 3 of the stripping section S. This oil from theflash tray is preferred to column bottoms or other bottoms material forthe reason that it is very nearly the equilibrium liquid of the ashsection vapors. When this condition obtains, the absorption oil effectof this oil recirculated with the feed stock through the heater is aminimum, permitting the distillation of the net overhead vapor cut at alower temperature than would be possible where column bottoms or otheroil less nearly in equilibrium with the vapors were employed.

When hydrocarbon oils are heated to high temperatures, especially in thehotter portions of the heater system, naphthenic acids, hydrogensulphide and other materials are formed which are corrosive to theheater surfaces. In order to eliminate corrosion resulting from theformation of these corrosive substances in the heated oil, it hasheretofore been the practice to introduce a quantity of a causticsolution into the feed material entering the heater. It has beendiscovered, however, that at the point in the heater where the excessWater in the said caustic solution flashes, an excessive amount ofcorrosion takes place. It has been found that this diiculty can beovercome by introducing thev caustic solution into the heated feed aShortdistance from the entrance to the fractionating column as shown atIlil. The feed line to the fractionating column at this point is a largeone and it has been found practicable to introduce the small amount cfcaustic solution necessary by means of a special connection as shown inFigure 2 into the central portion of the feed stream flowingtherethrough. Apparentlywith this arrangement and due to the highvelocity of the feed materials at this point and the size of theconnection, the thus introduced caustic solution is able to flashentirely within the oil stream without contacting any of the feed lineor fractionating equipment surfaces.

A large percentage of this iiashed caustic s'olution is retained in theunvaporized oil withdrawn from the flash section of the-fractionatingcolumn and this material is then introduced into the heating system byway of the hereinbefore described recirculating oil which is withdrawnfrom the flash section and returned to the heater. Thus only preflashedcaustic solution is allowed to enter the heater tubes.

The caustic solution to be introduced into the heated feed is withdrawnfrom the caustic supply tank C by means of pump lil and deliveredthrough line H2 to the point of introduction lill.

An auxiliary by-pass connection H3 is provided for introducing causticsolution directly into the heater by way of line 32 if desired.

Normally, control of the distillation system is accomplished, ashereinbefore stated, by Withdrawing predetermined fixed quantities ofgas oil and side cuts to production, allowing the quantity of refluxreturned to the column and the quantity of bottoms Withdrawn from thefractionating column to vary with Variations of input of heat andquantity of feed to the fractionating system. For example, the valve 56is manually .regulated to allow a predetermined quantity of gas oil tobe withdrawn to production and the valves corresponding to valve 99 onthe strippers adjusted for the withdrawal of predetermined quantities ofstripped side cuts, and the quantity of feed introduced into the heaterthrough the feed line 2l and the temperature of the heatedfeedintroduced into the fractionating system through inlet 28 ismaintained manually to approximately meet these arbitrarily setconditions. The quantity of recirculated cooled gas oil to the heatexchange trays V` is also regulated and fixed by means of valve 52.

Any irregularity in the quantity and temperature of feed is thenautomatically compensated for by corresponding variations in thequantity of reflux returned to the top of the fractionating section ofthe fractionating column and the quantity of bottoms withdrawn from thestripping section of the fractionating column. When, due to irregularityof firing of the heater, or for any other reason, the temperature of thefeed to the fractionating column is increased, the attendant increase inoverhead vapors will result in a greater quantity of fractionated vaporsbeing condensed in the heat exchange section of the fractionatingcolumn. This increased quantity of condensate Withdrawn from the heatexchange trays along with the recirculating cooling gas oil, will resultin an increased accumulation thereof in tank T, since the quantity ofgas oil withdrawn to production and the quantity of gas oil recirculatedto the heat exchange section of the column is a predetermined xedquantity. This increasein quantity of condensate accumulating in surgetank T Will result in a rise in the liquid level and will act throughthe iioat control therein to regulate valve 56 to allow, in turn, acorrespondingly greater quantity of condensate to be returned forrefluxing to the top of the fractionating section F of the fractionatingcolumn. Thus Variations of heat input to the column will automaticallybe compensated by corresponding Variations in quantities of heatabsorbing reflux.

The diificulties normally associated with an overhead tubular oilcondenser for the condensation of fractionated vapors have beeneliminated by the employment of the set of heat interchanger trays asshown at I4 and I5 in the top of the column as hereinbefore described.In this section of the colunm substantially total condensation of thefractionated vapors occurs by contacting them with cool recycled oil.This condensation is accomplished by the exchange of the latent heat ofvaporization of the said fractionated vapors for the sensible heat ofthe said recycled oil. The condensate commingles With the oil in theheat exchange section of the column and is Withdrawn therewith from thecolumn. No fractionation occurs in this section of the column asevidenced by the fact that the quality of the liquid leaving the lowerinterchanger tray is substantially the same as that of the vaporsentering the tray. In other words, the recycled cooling oil, thecondensate resulting from the condensation of the fractionated vapors,the reflux returned to the top of the fractionating co1- umn and the gasoil withdrawn to production are all of the same characteristics andquality.

In initiating operations of the fractionating system it is necessarythat a cooling medium be supplied to the heat exchange section of thecolumn in order to establish initial condensation of the vaporized feedmaterial, otherwise the vapors may pass through and out of the columnwithout condensation or fractionation. For this purpose a connection H5with valve H6 is provided for making connection to an outside supply ofgas oil, whereby a sufficient quantity may be introduced into thecooling oil circulating system to initially establish circulation ofthis condensing medium through the heat exchange section E of the columnand the cooler 41. Surge tank T may have sucient gas oil storagecapacity to provide for thus establishing operating conditions aftershut-downs.

Variations vin the quantities of feed, other factors being constant, aretaken care of by variations in the quantity of bottoms produced whichare automatically withdrawn through float controlled valve 36 ascontrolled by float control 3S.

An example of operation is as follows:

A topped Santa Fe Springs residium having a viscosity of 348 sec. at 122F. is introduced into the heater H at a preheated temperature of 350 F.,at a rate of 1804 barrels per 24 hours. The feed, after passing throughthe heater, is introduced into the flash section of the fractionatingcolumn at 28 at a temperature of approximately '715 F. Unvaporized oilis withdrawn from the flash tray at 30 and recirculated through theradiant tubes of the heater and reintroduced into the fractionatingcolumn with the feed at a rate of approximately 3500 barrels per 24hours. Approximately 3750 barrels per 24 hours of gas oil at 115 F. isrecycled to the heat exchange trays and approximately 604 barrels per 24hours of reflux returned to the top of the fractionating section. Thetemperature of the coolest heat exchange tray is thus maintained atapproximately 200 F. and the steam and xed gases are exhausted from thetop of the column at approximately this same temperature and at apressure of 29.1 in. vacuum. Approximately 2 gallons per hour of causticsolution is introduced into the heated feed to the fractionating system.Under these conditions 255 barrels of gas oil having a Viscosity of 145sec. at 100o F., 529 barrels per 24 hours of lubricating oil distillatehaving a viscosity of 244 sec. at 130 F., 322 barrels per 24 hourshaving a viscosity of 124 sec. at 210 F., 151 barreis per 24 hours oflubricating oil distillate having a viscosity of 355 sec. at 210 F. and537 barrels per 24 hours of bottoms from the stripping section of thefractionating column are produced.

The foregoing described process and apparatus is merely illustrative andthe invention is not limited thereby, but may include any process andapparatus which accomplishes the same within the scope of the invention.

We claim:

l. In a process for distilling oil the steps comprising heating the oil,introducing the heated oil into a flashing zone, initially passing thesaid heated oil in said flashing zone over a single ash tray throughwhich heated hydrocarbon vapors and steam pass, withdrawing a portionthe unvaporized oil from said flash tray, said oil being in substantialequilibrium with the vapors leaving the flashing Zone, commingling andheating the said withdrawn oil with the initial feed oil passing to thesaid ilash tray, separately stripping the balance of the unvaporized oilfrom the flash tray in countercurrent contact with steam and contactingall of the resultant stripping vapors with all of the heated oil on theflash tray in a single pass over said tray, said resultant vaporsconstituting the first mentioned hydrocarbon vapors and steam, andwithdrawing a bottoms product which is substantially heavier than thesaid withdrawn unvaporized oil from the ilash tray.

2. A process as in claim l in which the unvaporized oil withdrawn fromthe flash tray is commingled with the initial feed oil at anintermediate point in the heater.

3. In a process for distilling oil the steps comprising heating the oil,introducing the heated oil into a flashing zone, initially passing thesaid heated oil in said flashing zone over a single flash tray, throughwhich heated hydrocarbon vapors and steam pass, withdrawing a portion ofthe unvaporized oil from said ilash tray, said oil being in substantialequilibrium with the vapors leaving the flashing zone, commingling thesaid withdrawn oil with the initial feed oil introduced into the saidflashing zone, separately stripping the balance of the unvaporized oilfrom the ilash tray in countercurrent contact with steam and contactingall of the resultant stripping vapors with substantially all of theheated oil on the flash tray, said resultant vapors constituting thefirst mentioned hydrocarbon vapors and steam, and withdrawing a bottomsproduct which is substantially heavier than the said withdrawnunvaporized oil from the ilash tray.

4. In a process for distilling oil, the steps comprising heating theoil, introducing the heated oil into a ilash vaporizing zone andseparating vapors and unvaporized oil in said flash vaporizing zone,withdrawing vapors and unvaporized oil from said flash vaporizing Zone,said withdrawn oil being in substantial equilibrium with said vaporsleaving said ilash vaporizing zone, circulating a portion of saidwithdrawn oil which is in substantial equilibrium with said vaporsleaving the flash vaporizing zone through a heating Zone and back tosaid ilash vaporizing zone, commingling fresh feed with said circulatingequilibrium oil passing to said flash Zone, said combined circulatedunvaporized oil and said fresh feed constituting said lrst mentionedheated oil, introducing another portion of said unvaporized equilibriumoil from said ilash vaporizing zone into a stripping zone in contactwith steam, withdrawing steam and vapors from said strippingv zone andpassing substantially all of said withdrawn stripping steam and vaporthrough and in intimate contact with substantially all of said heatedoil in said flash vaporizing Zone, cornmingling the said stripping steamand vapors from the stripping zone with the resultant flashed vaporsreleased from said heated oil in the flash zone, said combined steam andvapors constitut` ing the rst mentioned separated vapors leaving theflash vaporizing zone, and withdrawing a bottoms product from saidstripping Zone which is substantially heavier than the said unvaporizedoil withdrawn from the ilash vaporizing Zone.

5. A process according to claim 4 in which the said contact of all ofthe said stripping steam and vapors from the stripping Zone withsubstantially all of the said heated oil in the said ilash vaporizingzone is effectively not more than a single stage of fractionation.

BLAIR G. ALDRIDGE. EDWARD G. RAGATZ.

